[RTADPA BW Tests] Assorted improvements

Assorted improvements:

Cherry-pick 4aa5ebd9 from master

• This seems to not be present in 2025-patches and provides a speed-up in BW tests
• Fix a bug in the logic of this section for evt_max = -1

Address lhcb-datapkg/PRConfig#42 (closed)

• Refactor to avoid chained assignment
• Use df.styler.map in favour of deprecated df.styler.applymap

Fix the link to the ROOT file in the monitoring page

Remove a duplicated Gaudi option in line_and_stream_rates.py

Fix logic for downloads using evt_max = -1

• Previously a max_size was determined proportional to evt_max
• If evt_max = -1 this max_size is negative and files won't download
• This was noticed on recent spruce_latest_bandwidth tests
• Along with lhcb-datapkg/PRConfig!570 (closed), this will revive spruce_latest_bandwidth if hlt2_bandwidth is switched back on

Pages: https://jconnaug-bwtests.web.cern.ch/Moore4993_smallimprovements/